NPS and DN relate as what?

• A. Nominal vs metric equivalent
• B. Nominal pipe size vs diameter
• C. National pipe standard vs design number
• D. Diameter number vs design number

Answer: (A)

NPS and DN are both nominal size designations used for pipes, but they express the same rough bore in different unit systems: NPS is the nominal pipe size in inches, while DN (Diameter Nominal) is the nominal size in millimeters. They relate by roughly multiplying the NPS value by 25.4 to get the DN value (with rounding to standard DN numbers). For example, 1/2 inch NPS is about DN 15, 1 inch NPS is about DN 25, and 2 inches NPS is about DN 50. The key idea is that these are nominal sizes, not precise inner or outer diameters, and they map between imperial and metric conventions.